1. Field of the Invention
The present invention concerns a method for machine-cut working of workpieces with rotationally symmetrical surfaces, particularly of crankshafts, which are chucked between tips at both ends unmachined at the peripheral circumference, of which at least one is axially adjustably deliverable, whereby for machine working of the two ends of the workpiece the respectively oppositely located end is clamped radially with chuck means, while at the workpiece end to be machined the radial chuck means are axially retracted, of which the one radial chuck means has centering and the other radial chuck means has equalizing compensation clamping chuck elements, whereby after the end machining the median region of the workpiece is machined, while both radial chuck means engage against the workpiece ends.
The apparatus for carrying-out such a method includes two oppositely located main spindles and chucks, which have radially and axially adjustable chuck elements, and with two oppositely located centering tips which are adjustable axially relative to the chuck elements respectively the chucks.
2. Description of the Prior Art
With a known method of German Offenlegungsschrift 38 09 619 there is machine working of the workpiece at both ends sequentially in time. In order to be able to machine an unmachined workpiece end at the peripheral circumference, it is held only with a centering tip, while the oppositely located workpiece end which is likewise unmachined at the peripheral circumference, is clamped by means of jaws of a jaw chuck, which can be moved radially independently of each other. This jaw chuck forms a radial clamping chuck means with equalizing clamping chuck elements. The oppositely located clamping chuck means has radially centering clamping chuck elements, which initially are axially retracted. Thereby the adjoining workpiece end can be machined on the peripheral circumference with a corresponding tool.
Subsequently the oppositely located workpiece end is machined. Additionally hereto the workpiece end previously machined on the peripherally circumferential side is securely held by means of the radially centering clamping chuck means and the centering tip, while now the other still to be machined workpiece end is held only by a centering tip. The equalizing clamping chuck elements are axially retracted. If also this workpiece end is machined at the peripheral circumference, the workpiece is securely held at both ends by means of the clamping chuck means as well as the centering tips. This clamping tension between the tips remains also during the central-median machining of the workpiece. Since with this central-median machining both the clamping chuck means as well as also the centering tips engage against the workpiece at the previously machined workpiece ends, there exists at both workpiece ends a conformity determination. If the axes of the tips as well as of the centering clamping chuck elements do not coincide exactly, then constraining pressure forces occur which encumber and burden the centering tips. Consequently very strong load burdening of the apparatus and of the workpiece occur and are encountered. The apparatus is subjected to a strong wear, while the workpiece ends because of these load burdens have too great rotational tolerances.
Equalizing clamping chuck elements, which clamp equalizingly to the workpiece center, represent a compromise, since the rotational accuracies at the clamping diameter are comparatively small and nominal.